1. Field of the Invention
This invention relates to a rotating motor-generator voltage controller for a turbocharger incorporated in a motor-generator mounted on the turbocharger shaft.
2. Description of the Prior Art
Many designs have been proposed which mount a turbocharger to the exhaust of an engine and directly connect a motor-generator to the turbocharger shaft in order to recover the exhaust energy, and a number of these proposed designs have been implemented. This design fundamentally consists of a rotating motor-generator mounted to the turbocharger which functions as a motor or a generator. The operation mode changes according to the operation status of the internal combustion engine. For example, when the internal combustion engine is operating under high load, the motor-generator is operated in the motor mode, assisting compressor rotation which in turn enhances turbocharger operation. On the other hand, when the internal combustion engine is operating at a high rpm, the large volume of exhaust gas which is discharged is transfered into rotating force by the turbine which turns the compressor, and the revolving motor-generator is operated in the generator mode in order to recover the exhaust gas energy and convert it into electric energy. Design proposals of this type have been published repeatedly, as disclosed in Japanese Laid-Open Publication No. 1-155027 published by the Japanese Patent Office.
The turbocharger unit described above consists of a voltage converter which converts 12 V DC into 100 V AC, a rectifier which converts 100 V AC into 70 V DC, an inverter which converts 70 V DC power and outputs it as variable frequency 3-phase AC power, and a low-voltage rectifier which converts the 3-phase AC voltage recovered by the generator into 12 V power.
Furthermore, when the rotating motor-generator in this turbocharger is functioning as a generator, the low-voltage rectifier operates, converting the electric power generated into 12 V DC power. When the rotating motor-generator is operated as a motor to drive the compressor, the AC output with the required frequency and waveheight is obtained after a step where the 12 V DC power is boosted to 100 V AC by the voltage converter, another step where the 100 V AC power is converted to 70 V DC, and another step where the 70 V DC power is converted into 3-phase AC output, enabling operation of the rotating motor-generator as a motor.
As explained above, with conventional turbochargers, the voltage applied to the motor had to be converted from DC to AC to DC to AC when the rotating motor-generator was operated as a motor, requiring an extremely complicated circuitry configuration. This inevitably led to high production costs, a high level of difficulty to perform assembly and adjustment, and large dimensions.